1. Field of the Invention
The invention relates to extrudable, low-migration organic silicone copolymers of high transparency, and to their preparation and use.
2. Background Art
To produce abhesive coatings, curable polyorganosiloxanes are applied to substrate materials and then cured through use of thermal energy or radiation. Curing of the coating material is frequently the rate-determining step in the production of adhesive substrate materials. Additionally, it is necessary to install drying ovens or UV or IR lamps, whose operation is highly energy-consuming. Accordingly, more recent developments have been aimed at providing coating materials which allow this curing step to be omitted.
EP-A 168624 describes the coextrusion of PP backing films with an anti-adhesive layer comprising a polydimethylsiloxane. EP-A 541103 discloses coating of laminated PET films by application of emulsions of polysiloxane-polyvinyl graft polymers, the polysiloxane component being composed of a cyclic siloxane and a siloxane containing a free-radically polymerizable group, in the presence of which the vinyl monomers are polymerized. EP-A 254050 describes the production of a release liner by extrusion of a reaction product of H-siloxane and a hydrocarbon compound containing at least one ethylenically unsaturated group.
U.S. Pat. No. 5,086,141 discloses a crosslinked polysiloxane-styrene/butadiene copolymer obtained by polymerizing styrene and butadiene in the presence of a difunctional polysiloxane. WO-A 96/39459 describes block copolymers of ethylene and cyclic siloxane monomers which can be used in coextrusion for release liners. By blending with HDPE, release liners having good abhesive properties may be obtained. WO-A 95/00578 discloses coextrusion-prepared copolymers of monofunctional silicones and functionalized polyolefins, which can be used as release material. WO-A 91/15538 describes release films comprising a base polymer and a silicone copolymer which is composed of a hard organic polymer segment and a soft polydialkylsiloxane segment. This copolymer is admixed with the base polymer as an additive.
EP-A 352339 describes protective coatings for concrete constructions, comprising copolymers of divinyl-polydimethylsiloxane with acrylate or methacrylate esters and with vinyl-functional or acryloyl-functional alkoxysilanes, as a solution in organic solvents. Thermally curable acrylic resins supplied as a solution in organic solvents, useful for coating metals, especially stainless steel, are the subject matter of EP-A 159894. To improve adhesion to metals, in particular to prevent flaking of the coating when coated metal parts are deformed, acrylic resin solutions of copolymers of (meth)acrylates, hydroxy-functional or epoxy-functional (meth)acrylates, vinyl-functional polysiloxanes, and vinyl-functional silanes are used. To improve adhesion the polymers are subjected to post-crosslinking catalyzed by organotin compounds, and are cured thermally.
U.S. Pat. No. 3,879,491 discloses modified thermoplastics obtained by polymerizing ethylenically unsaturated monomers in the presence of polydiorganosiloxanes. U.S. Pat. No. 4,985,155 relates to a textile treatment composition based on a graft copolymer obtained by polymerizing acrylates or meth-acrylates in the presence of a polydiorganosiloxane bearing moieties containing ethylenically unsaturated double bonds. DE-A 3706095 describes the preparation of resins containing polysiloxane units by polymerizing a vinyl monomer in the presence of a double-bond-functionalized polysiloxane which contains at least two hydroxide and/or amine functional groups.
DE-A 10064092 pertains to polyorganosiloxanes for producing abhesive coatings which do not require addition of thermal energy or radiation to cure. The polyorganosiloxanes are silicone block copolymers containing a crosslinkable hard-segment polymer component and a soft-segment polyorganosiloxane component. These silicone block copolymers are prepared by reactive coupling of the block segments or by polymerization of the hard segment component in the presence of the polyorganosiloxane.
The products known to date, however, frequently exhibit unsatisfactory abhesive properties, migration of silicone from the release layer or low substrate adhesion, or are difficult to obtain by synthesis. Moreover, they often possess no transparency, since the silicone component and the organic polymer component are incompatible, leading to the formation of domains or to phase separation. Furthermore, the known products often cannot be applied by means of extrusion. In many cases the organic silicone copolymers described are too highly crosslinked and can no longer be processed as thermoplastics.